Recently, new mineral reservoirs have been discovered at great ocean depths which are not sufficiently productive to merit use of large scale deep sea tension-leg platform structures. Therefore, smaller, less expensive production platforms have been developed which can be transported from one mineral reservoir to another. These platforms use tension-leg mooring, like conventional tension-leg platforms (TLPs), but comprise smaller floatation structures. An example is disclosed in Monopod TLP Improves Deepwater Economics, PETROLEUM ENGINEER INTERNATIONAL (January 1993), incorporated herein by reference. Single-piece tendons are used which comprise a length of solid metal with buoyancy devices attached at each end. The tendons are towed to the production site and upended by flooding the lower permanent buoyancy tank. The upper permanent buoyancy tank is oversized so the tendons can be left self-standing. Permanently attached buoyancy tanks make premature detachment impossible. The structure of the TLP is then ballasted by a large derrick and lowered to the previously installed tendons and then deballasted to fully tension the tendons.
Single-piece tendon systems, however, are costly to install and remove. All of the tendons for a given TLP must be installed before the TLP can be attached to the tendons. The TLP must then be ballasted so that it sinks down to the depth of the tendons so that it may be attached to all of the tendons at the same time. Because the TLP is free floating and unstable, it becomes difficult to make the connections between the TLP and the tendons. This means that a very large derrick barge must be brought to the operation site each time the TLP is assembled or disassembled.
Therefore, there is a need for a device and process which more easily attaches a TLP to the tendons.